1. Field of the Invention
The present invention concerns an apparatus and a method of coating a substrate by coating a slurry and extending the coated slurry along a plurality of flow channels formed in parallel to a substrate and, more in particular, the method is suitable to preparation of a catalyst by coating a catalyst slurry to the inner wall of honeycomb flow channels formed to a monolith as a catalyst for use in an exhaust gas purifying catalyst.
2. Statement of Related Art
As a method of uniformly coating a catalyst slurry with no loss to the inner wall of the honeycomb flow channels formed in a monolith as a catalyst substrate, a vacuum coating method of sucking and coating a previously metered slurry has been known, for example, in JP No. 2737837 (Patent Document 1).
In this Patent Document 1, as shown in FIG. 8(a), after supplying a previously metered slurry S in a slurry container 51, open ends of honeycomb flow channels 53 of a monolith M as a catalyst substrate are brought into contact with a liquid surface 52 of the slurry with the ends being downward, and the slurry S is sucked from the upper end openings of the honeycomb flow channels 53 by vacuum sucking, and the slurry S is introduced uniformly into each of the honeycomb flow channels 53, 53, . . . by a predetermined metered amount.
In this case, since no excess slurry is deposited to the monolith M, troubles of removing, recovering or recyclically using the surplus portion can be saved.
However, as shown in FIG. 8(b), in the case of sucking the slurry under vacuum from the upper end of the monolith, since honeycomb flow channels 53B at the central portion suck more slurry S than the honeycomb flow channels 53A in the peripheral portion, this results in a problem that the flow channels can not be coated with a uniform coating length, for example, in a case of intending to coat the one-half length of the honeycomb flow channels 53 with the slurry S.
Further, in a case of controlling the vacuum degree for each of a plurality of honeycomb flow channels individually thereby controlling the amount of the slurry S to be entered, it is theoretically possible to suck an identical amount of the slurry S to the respective honeycomb flow channels and coat them each for a uniform length, but this complicates the mechanism and the control therefor and can not be practiced actually.